1. Field of the Invention
The invention relates to a process for replacing one or two hydrogen atoms or one hydrogen and one chlorine, bromine or iodine atom attached to a benzylic carbon atom of an aromatic compound with one or two fluorine atoms, using a mixture of hydrogen fluoride (HF) and a metal oxide which is lead dioxide (PbO.sub.2) or nickel dioxide (NiO.sub.2) at -30.degree. to +80.degree. C. The starting aromatic compound has one or more alkyl or halogenated alkyl or halogenated alkyl side chains and one or more electron-withdrawing groups such as nitro, carboxy, formyl and the like.
2. Prior Art
U.S. Pat. No. 2,436,143 to H. H. Hoehn discloses the reaction of a fluoroalkane containing at least two carbon atoms and from one to two fluorine atoms on a terminal carbon atom with a mixture of lead dioxide, manganese dioxide or cobaltic oxide and HF to produce a more highly fluorinated alkane. In the process the entering fluorine atom always attaches itself to the terminal carbon already bearing a fluorine atom so the resulting fluoroalkane possesses at least two fluorine atoms on the terminal carbon.
U.S. Pat. No. 2,466,189 to T. P. Waalkes, and A. L. Henne and T. P. Waalkes, J. Amer. Chem. Soc. 67, 1639 (1945), disclose the reaction of an olefin with lead dioxide and HF whereby two fluorine atoms are added to the double bond to produce a saturated compound.
German Offenlegungsschrift 2,140,699 uses lead dioxide and HF to add fluorine across the double bond of an olefinically unsaturated polymer.
E. R. Bissell et al., J. Org. Chem. 29, 1591 (1964) use lead dioxide and sulfur tetrafluoride to add fluorine across the double bond of a halogenated olefin.
U.S. Pat. No. 3,379,780 to R. E. Robinson discloses a fluorination process using HF, a oxygen-containing gas, and a noble metal of Group VIII. No lead dioxide or nickel dioxide is shown.
U.S. Pat. No. 3,214,482 to Caropreso et al. discloses ferric halide as a chlorination, bromination or iodination catalyst for hydrocarbons.
French Pat. No. 2,254,558 discloses the reaction of an aromatic compound such as p-CH.sub.3 COC.sub.6 H.sub.4 NO.sub.2 with MoF.sub.6 in the presence of BF.sub.3 to produce p-CH.sub.3 CF.sub.2 C.sub.6 H.sub.4 NO.sub.2.
None of the prior art show the present invention where one or two fluorine atoms replace one or two hydrogen atoms or one hydrogen and one chlorine, bromine or iodine atom on a benzylic carbon atom of an aromatic compound.